1. Field of the Invention
The present invention relates to user-programmable antifuse structures. More particularly, the present invention relates to a metal-to metal antifuse structure with improved immunity to electrode diffusion through a barrier layer interposed between the electrodes and the antifuse material. The present invention relates to processing methods, in general, and the selection of diffusion barrier materials, in particular, to ensure manufacturability of products containing metal/a-Si/metal antifuses
2. The Prior Art
Antifuses employing amorphous silicon antifuse material are known in the prior art. Since such antifuses are often deployed between metal layers in an integrated circuit, they may employ materials such as aluminum as the antifuse electrodes. Traditionally, several methods have been employed to form barrier layers between the electrodes and the amorphous silicon antifuse material. A thin layer of deposited silicon dioxide has been used. If this layer is too thin, it will not be an effective barrier, and if it is too thick, it will appreciably raise the programming voltage of the antifuse. Control of the thickness of this layer is a difficult task. Alternatively, the lower electrode has been formed from TiW itself.However, this layer cannot be used as the bottom layer of the antifuse and as an interconnect layer. A silicon nitride layer has also been deposited over the TiW layer. If this layer is too thin, it will not be an effective barrier, and if it is too thick, it will appreciably raise the programming voltage of the antifuse.
While titanium-tungsten (TiW) has been used as diffusion barrier for fabrication of antifuses comprising an amorphous silicon antifuse material sandwiched between two metal layers, TiW is not an effective diffusion barrier; especially for use in process technologies which employ alloy temperatures of about 400.degree. C. to 450.degree. C. or higher, because aluminum diffuses through the barrier layer to the amorphous silicon and changes its conductive properties. In addition Ti or W atoms may also diffuse into the amorphous silicon antifuse layer, altering its conductive properties.